The Listing Number Is (Often) a Trap
Real estate listings show the seller's most recent tax bill. That number reflects the seller's assessed value, the seller's exemptions, and in many states, years of caps that kept their assessment far below market value. None of that transfers to you.
The moment the sale closes, three things typically change:
- The assessment resets or catches up. In California, your purchase price literally becomes the new assessed value (Proposition 13). In Florida, the Save Our Homes cap resets. In Michigan, taxable value uncaps to 50% of market value.
- The seller's exemptions disappear. Their homestead, senior, or veteran exemptions were theirs, not the house's.
- You pay on what you paid. If the seller bought in 2009 and you're buying in 2026 at triple the price, your tax base can be triple theirs.
A Concrete Example (Florida)
| Seller's Bill | Your First Full Bill | |
|---|---|---|
| Assessed value | $210,000 (capped since 2012) | $415,000 (resets to market) |
| Homestead exemption | -$50,000 | -$50,000 (once you apply!) |
| Taxable value | $160,000 | $365,000 |
| Rate (18 mills) | 1.8% | 1.8% |
| Annual tax | $2,880 | $6,570 |
Same house, same rate, same exemption. The bill more than doubles anyway, purely because the assessment resets to your purchase price. If you budgeted your mortgage payment around $2,880, you now have a $300-per-month problem.
How to Estimate Your Real Bill in 4 Steps
Step 1: Use Your Expected Purchase Price, Not the Current Assessment
In reset states (California, Florida for capped properties, Michigan), your purchase price is the best predictor of your new assessed value. In states without resets, look at what the assessor's current market value estimate is versus recent sale prices in the neighborhood; if assessments lag the market badly, expect yours to catch up at the next reassessment cycle.
Step 2: Find the Actual Local Rate
Don't use a state average. Rates vary enormously within states, sometimes across a single school district line. Look up the combined millage for the specific city and county on our state and county pages, or find a recent tax bill for a nearby recently-sold home on the county's property search portal (they're public records in most states).
Step 3: Subtract the Exemptions You Will Actually Qualify For
Apply the homestead exemption only if this will be your primary residence, and remember you usually need to occupy by January 1 and file an application. Second homes and investment properties typically get no exemption and, in some states like Georgia and South Carolina, get assessed at a higher ratio too.
Step 4: Do the Math
(Purchase price × assessment ratio − exemptions) × combined local rate = your estimated annual bill
Then divide by 12 and add it to your projected mortgage payment. If the lender requires escrow, this is roughly what they'll collect monthly, though their first-year estimate may be based on the seller's old bill, which means an escrow shortage surprise in year two. Our guide on how escrow works covers that scenario.
Questions Worth Asking Before You Offer
- When was this property last reassessed, and what triggers reassessment here: sale, cycle, or both?
- What exemptions is the seller currently receiving?
- Are there any special assessments on the property (sewer bonds, Mello-Roos in California, MUD taxes in Texas suburbs)? These can add thousands and don't show up in the millage rate.
- Is a school bond referendum on the ballot in this district?
Your buyer's agent can get all of this. The listing agent has answers too, though their incentive is to keep the tax number looking small.
Bottom Line
Estimate your property taxes from your purchase price and the actual local rate, never from the seller's bill. In reset states the difference can be 50-100%+. Five minutes with our calculator before you write the offer beats a nasty letter from your escrow servicer a year after closing.